1. Field of the Invention
The present invention relates to non-aqueous electrolyte rechargeable batteries.
2. Description of the Related Art
Electronic devices of small size such as laptop computers or notebook computers as portable personal computers, mobile phones or cell phones as portable telephones, digital cameras, etc. have become widely used. Because such small electronic devices of small size have spread and progressed, rechargeable battery (secondary battery) demand is also increasing around the world. Lithium ion batteries are a commonly used type of rechargeable battery with a global market.
Those small electronic devices of small size require rechargeable batteries, for example, non-aqueous electrolyte rechargeable batteries such as lithium-ion rechargeable batteries which are one of the most popular types of rechargeable batteries for portable electronics because of their high capacity.
There have been studies to apply such a non-aqueous electrolyte rechargeable battery to various types of vehicles and home power sources which need a large amount of electric power. For example, there are electric vehicles (EV, or electric drive vehicles), hybrid vehicles (HV, or hybrid electric vehicles), plug-in hybrid vehicles (PHV, or plug-in hybrid electric vehicles), home energy management system (HEMS), etc. In order to have a large amount of electric power, it is necessary for the non-aqueous electrolyte rechargeable battery to have a plurality of battery cells. Each of those battery cells has electrodes comprised of a plurality of large-sized electrode plates which are stacked to form a laminate.
Because lithium-ion rechargeable batteries as one type of non-aqueous electrolyte rechargeable batteries have superior reversibility to intercalate and de intercalate (charges and discharges) lithium ions, it is possible to use lithium-ion rechargeable batteries repeatedly. For example, patent document 1, Japanese patent laid open publication No. 2007-95443, has disclosed such a lithium-ion rechargeable battery.
Patent document 1 has disclosed a non-aqueous electrolyte rechargeable battery composed of a positive electrode, a negative electrode and non-aqueous electrolyte. This non-aqueous electrolyte rechargeable battery is configured to have a structure in which:
the positive electrode and the negative electrode are made of material capable of intercalating and deintercalating lithium ions;
a charge capacity ratio (capacity of the negative electrode 12/the capacity of the positive electrode 11) is within a range of 1.0 to 1.15 until a positive electrode potential reaches 4.5 volts (vs. Li/Li+); and
a principal component of an active electrode material forming the positive electrode active material is a lithium transition metal composite oxide expressed by a formula of LiaMnsNitCouMovO2, where 0<=a<=1.2, s+t+u=1, 0<s<=0.5, 0<t<=0.5, 0.45<=s/(s+t)<=0.55, 0.45<=t/(s+t)<=0.55, u>=0, 0.001<=v<=0.01.
The positive electrode active material (as positive electrode material) in a conventional non-aqueous electrolyte rechargeable battery does not have adequate safety. Specially, a crystal structure of the lithium transition metal composite oxide used in the positive electrode active material is destroyed due to a long time of use, and oxygen contained in the lithium transition metal composite oxide releases.
In order to solve this problem, there have been proposed non-aqueous electrolyte secondary batteries containing composite oxide material as a positive electrode active material expressed by a formula of Li2-xNiαM1βM2γO4-ε, where 0.50<α<=1.33, 0<=β3<0.67, 0<=γ<=1.33, 0<=ε<=1.00, M1 is at least one of Co, Al and Ga, M2 is at least one of elements expressed by Mn, Ge, Sn and Sb, and the variable x in the formula varies within a range of 0<=x<=2 by intercalating and deintercalating lithium ions.
However, the positive electrode made of a positive electrode active material expressed by Li2-xNiαM1βM2γO4-ε, increases its resistance in a low SOC region. The increasing of the positive electrode resistance deteriorates performance of the non-aqueous electrolyte secondary battery when the charge and discharge of the non-aqueous electrolyte secondary battery using the positive electrode made of a positive electrode active material expressed by Li2-xNiαM1βM2γO4-ε, is performed in the low SOC region. This means that the deterioration of battery performance of the non-aqueous electrolyte rechargeable battery as the lithium-ion rechargeable battery is generated in the low SOC region. The deterioration of battery performance of the non-aqueous electrolyte secondary battery occurs in the low SOC region.